1. Field of the Invention
The present embodiment relates to a glass base manufacturing apparatus and method thereof. More particularly, the present embodiment relates to a glass base manufacturing apparatus and method thereof for manufacturing a glass base material, which is a base material of an optical fiber.
2. Description of the Related Art
FIG. 1 shows the configuration of a conventional glass base material manufacturing apparatus. A glass base material manufacturing apparatus has a chuck 12 and burners 22A-22D. A chuck 12 hold the both ends of the starting base material 2. Furthermore, a chuck 12 rotates the starting base material 2 around the axis of the starting base material 2. The burners 22A-22D are arranged at equal intervals in the row along the longitudinal direction of the starting base material 2. Raw material gas, fuel gas, and assist combustion gas are supplied to the burners 22A-22D. The burners 22A-22D hydrolyze the supplied raw material gas while moving reciprocatory along the longitudinal direction of the starting base material 2 and ejecting glass soot to the starting base material 2. The deposit 10 is formed by depositing glass soot around the starting base material 2 with the burners 22A-22D.
The glass base material used as base material of an optical fiber is manufactured by heat-treating and vitrifying the glass soot deposited on the circumference of the starting base material 2. An optical fiber preform is obtained by elongating and reducing the diameter of a glass base material to the form suitable for drawing, and an optical fiber is manufactured by drawing the glass base material.
FIG. 2 shows a deposit amount of the glass soot by the burners 22A-22D according to a full-range traverse method. In the case of the full-range traverse method, all the burners 22A-22D move reciprocatory from one end of a region, on which glass soot is deposited, to another end of the region while moving beyond an effective part, which can be effectively used as a glass base material product. Furthermore, each burner 22A-22D deposits glass soot for a specific deposit amount at uniform thickness within the range of the effective part. Therefore, the whole thickness of the deposited glass soot becomes substantially uniform along the moving direction of the burners 22A-22D even when the deposited amount of the glass soot of each burner 22A-22D is different, respectively.
FIG. 3 shows a deposited amount of the glass soot by the burners 22A-22F according to the partial traverse method. In the case of the partial traverse method, the burners 22A-22F deposit glass soot on the starting base material 2 while moving reciprocatory over a part of the section of the whole length of the starting base material 2. For example, the starting position of the reciprocate movement of each of the burners 22A-22F is shifted partially and sequentially, and glass soot is deposited on the starting base material 2 (as referred to in Japanese Patent Application Laid-Open No. 3-228845).
Since the partial traverse method can increase the number of the burners without increasing the unnecessary part, which cannot be used as a glass base material product, as compared with the full-range traverse method as shown in FIG. 2, the partial traverse method can increase the speed for depositing glass.
However, in case of the partial traverse method, each burner 22A-22F moves reciprocatory a part of sections of the whole length of the effective part. Therefore, as shown in FIG. 3, when the deposited amount of glass soot is different for each of the burners, the whole thickness of the deposited glass soot becomes uneven along the longitudinal direction of the effective part.
If the deposited amount of the glass soot along the longitudinal direction of the starting base material 2 is not uniform, the glass base material, which is generated by vitrifying the deposit 10, has a clad, which is deposited around a core, having a varied thickness.
Therefore, if a preform is manufactured by elongating and reducing the diameter of a glass base material having a clad, the thickness of which is not uniform, and an optical fiber, which is the final product, is manufactured by drawing the preform, the diameter of the core of the optical fiber will fluctuate. Since light propagates inside a core, if the core diameter is changed, a predetermined characteristic required for an optical fiber cannot be acquired. Therefore, when the deposited amount of glass soot is uneven along the longitudinal direction of the effective part, the process for grinding the part, where the thickness of the deposited amount is large, to make the thickness to be uniform becomes necessary, and the manufacturing cost thus increases.